This invention relates generally to the field of papermaking fabrics and more particularly to structures for making separable seams to join the ends of such fabrics.
Papermaking fabrics, both forming fabrics and the felts used for wet pressing and for drying are conventionally woven either as a flat length of fabric or as an endless loop or band. The flat woven fabrics necessarily must have their opposed ends joined to form the necessary endless band used on papermaking machines. The endless woven fabrics may either be loaded onto the papermaking equipment in the endless form, or may be flattened into a double thickness length of fabric, with the ends of that double thickness fabric then being joined to form the installed endless loop or band. Where seaming is required, an increasingly popular approach has been to provide a separable pin seam in which a pin or pintle is inserted between interengaged loops on opposed ends of the fabric. Examples of this structure are plentiful, as in Codorniu, U.S. Pat. No. 3,815,645, Gisbourne, U.S. Pat. No. 4,244,084 and in Crook, U.S. application Ser. No. 279,040 filed Dec. 1, 1988 now U.S. Pat. No. 4,896,702 and assigned to the assignee of this present application.
The removable pin seaming technique has become especially popular for press felts and dryer felts, due to the stiffness of those fabrics with their needled felt batt making them difficult to mount on the machinery in endless form. A particularly advantageous method of seaming such papermaking felt is disclosed in the Crook application Ser. No. 279,040 noted above. This technique utilizes two helical coils, with one each attached to the opposing ends of the base weave of the fabric. To seam this fabric the two coils are brought into interengagement with a pintle pin inserted therethrough to hold the seam closed. An alternative structure being investigated for seaming involves the use of slightly modified coils having locking heads formed thereupon to be mounted in a similar manner in a base weave to form a spiral zipper seam. This seam is generally similar in configuration to conventional plastic zippers commonly found on articles of clothing and is easily joined by a slider either of the conventional form, such as found on clothing, or in the form of modified pliers in which each jaw of the pliers carries one-half of the slider head.
While helical coil seaming arrangements, as noted above, have enjoyed substantial success when used on forming fabrics, they have experienced significant problems when incorporated in needled felts. These problems result from the material from which the helical coils are fabricated. In general, it has been found that, in order to form loops of sufficient rigidity to retain the seam, it has been necessary to fabricate the loops of a thermoset plastic monofilament, such as nylon or similar materials. However, when a coil manufactured of this type of material is subjected to the needling process to affix the felt batt to the base fabric, there is a high likelihood of a needle piercing one or more loops of the coil. Because of the use of this rigid monofilament, the piercing of a loop by one of the felting needles frequently either breaks the loop of the coil completely or damages it such that it will subsequently fail in the operating environment of the papermaking machine. This has limited the practicality of using the helical coil seaming technique on such felts.